Of mobile communication systems, by introduction of High Speed Downlink Packet Access (HSDPA), a Third Generation (3G) mobile communication system utilizing W-CDMA technology has been satisfying market demands for several years and now secured a competitive position against other systems. However, in the coming years, a long-term technological development is desirable to cope with rapidly increasing multimedia traffics and ubiquitous traffics. In standards of Third Generation Partnership Project (3GPP) that is a standards body, wireless communication systems defined as Long Term Evolution (LTE), or Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are gaining popularity. In LTE, a delay time is improved from about 10 ms to 5 ms or less compared to Third Generation (3G), and throughput is improved by a factor of 2 to 4 compared to HSDPA, improving utilization efficiency of frequency.
In considering improvement of accuracy in measurement for reception quality or reduction of circuit size on a mobile terminal side as described above, it is also desirable to consider a frequency operation of LTE, 3G, and the like on a network carrier side.
An operation of LTE cell reselection in 3GPP Release 9 is described below. The operation is described for a case where a mobile terminal located in a LTE serving cell is making the switch to 3G Universal Mobile Telecommunication System (UMTS). When threshServingLowQ is set in the system information block 3 to be transmitted from the LTE cell, it is stipulated that the operation is determined based on threshold determination of reference signal received quality (RSRQ). On the other hand, When the threshServingLowQ is not set, it is stipulated that the operation is determined based on the threshold determination of reference signal received power (RSRP).
Furthermore, in a case where a mobile terminal located in a UMTS serving cell is making the switch to LTE, it is stipulated that the operation is determined based on the threshold determination of RSRQ when both high2 of Threshx and low2 of Threshx are set in the system information block 19 of the UMTS cell. On the other hand, when either one of high2 of Threshx and low2 of Threshx is not set, it is stipulated that the operation is determined based on the threshold determination of RSRP. In this way, in 3GPP Release 9, the cell reselection operation is determined based on the threshold of RSRP or RSRQ.
Thus, when performing the threshold determinations of RSRP and RSRQ, it is desirable for the mobile terminal to carry out accurate reception quality measurements such as RSRP, RSRQ, and the like.
For example, Japanese Laid-open Patent Publication No. 2010-050557 discusses a technology that estimates noise power even when a desired signal and an interfering signal are overlapping to each other.